Continuing investigation of three basic hypotheses is planned in the second year of this three year project. These hypotheses include: (1) that physical conditioning alters membrane receptors for adrenergic or cholinergic hormones and drugs; (2) that different subtypes of cardiac beta adrenergic receptors exist and have differential effects on chronotropy and inotropy; (3) that tissue-specific alterations in membrane adrenergic receptors occur in response to a single stimulus.